The California Department of Corrections and Rehabilitation announced Wednesday that Phillips -- a former college star at Nebraska whose NFL career was derailed by off-the-field issues -- was found unresponsive in his cell at Kern Valley State Prison early Wednesday morning. He was transported to a local hospital where he was pronounced dead.

Phillips was 40. Prison officials are investigating the death as a possible suicide.

Phillips was facing the death penalty after being accused of murdering his cellmate in 2015. Phillips was initially incarcerated in 2008, when he was sentenced to over 31 years in prison after being convicted of "inflicting great bodily injury involving domestic violence, corporal injury to a spouse, false imprisonment and vehicle theft."

Phillips was a star tailback on Nebraska's national championship teams in 1994 and 1995. The Rams selected Phillips with the sixth overall pick in the 1996 NFL Draft, but he averaged just 3.4 yards per carry before being released midway through his second season. His NFL career ended in 1999 after short stays with the 49ers and Dolphins.